This invention has as its object an automatic advance device controlled hydraulically for a fuel injection system, in particular for a diesel engine injection pump.
It is known that in a diesel engine, in particular a large engine equipping a commercial vehicle, it is essential to introduce, in the kinematic chain of movement terminating at the shaft of the injection pump, a variable angular offset, taking into account instantaneous operating conditions of the engine. Automatic mechanical devices for adjustment of injection advance are known which, however, poorly withstand high driving stresses.
A hydraulic automatic device for advance adjustment is also known, in particular by French Pat. No. 2 445 440, for a diesel engine injection pump able to be fitted directly on the engine by a flange, the advance device able to be housed actually inside the distributor housing of the diesel engine. As it is described in this prior patent, the advance device comprises a hub integral with the injection pump, a housing surrounding the hub and comprising two rollers. An eccentric governor weight is mounted on the hub to be able to oscillate under the action of the centrifugal force. Two advance control pistons cooperate with the rollers to cause an angular offset between the hub and the housing. One of the pistons acts on the governor weight by a spring. The internal pressure of the device is adjusted automatically by a distributor with controlled relief.
In such a device, the injection advance is automatically controlled by the speed of rotation of the device, the centrifugal force acting on the governor weight taking a position of balance resulting from the centrifugal force acting on the governor weight and the tension of the spring. The oil pressure acting on the pistons is adjusted by the distributor controlled by the governor weight. In this hydraulic automatic device for injection advance of known type, an angular offset depending only on the speed of rotation is obtained.
It is necessary, however, to make other operating parameters of the engine and in particular the charge of the injection pump and/or the temperature of the hydraulic fluid intervene in the adjustment. The charge of the injection pump constitutes an operating parameter on which depends the pressure of the hydraulic fluid, which is directly proportional to the torque to be transmitted.